1. Field of the Invention
The present invention relates to an optical diffusing layer used in order to suppress decrease in visibility of a screen, an optical diffusing sheet having the optical diffusing layer concerned thereon, and further relates to an optical element in which the optical diffusing sheet concerned is prepared thereon, in a liquid crystal display (LCD), organic EL, and PDP, etc.
2. Description of the Related Art
Conventionally, in picture display, such as LCD, incidence from an indoor lighting, such as a fluorescent light, or sunlight from windows, or a reflection of operator's shadow etc. given to a display unit surface sometimes aggravates visibility of pictures. Therefore an optical diffusing layer is provided, on LCD surface, in which fine concavo-convex structure is formed in order to diffuse a surface reflected light, to suppress a regular reflection of outdoor daylight and to prevent a reflection of outside environment (having antiglare property), for the purpose of improvement in the visibility of pictures. As a formation method of optical diffusing layer, a method is mainly used in which a resin layer is formed with a coated layer having a resin containing particles in dispersed state, because fine structure may be easily realized and at the same time excellent productivity may be realized by the method.
In the case where an LCD is required a high definition (for example, no less than 120 ppi), however, when this LCD is equipped with the above-mentioned optical diffusing layer, a portion appears on the LCD surface that has glare and a different strength of brightness by an effect of convex lens effect demonstrated by a fine concavo-convex structure formed with particles projected on the surface of the optical diffusing layer. Consequently, decrease in visibility may be caused.
A technical indication is disclosed for example, in JP,9-193332,A and JP,9-193333,A that in order to solve such problems an average of peak-to-peak distance (Sm) of a surface with fine concavo-convex structure, and an average of center line surface roughness (Ra), etc. are to be adjusted in a specified range. However, in the technology, even if a surface with fine concavo-convex structure is controlled to have the above-mentioned property in the specific range, a defect of glare cannot necessarily be efficiently inhibited.